The ground moves due to several natural and human-caused phenomena. Key causes of ground movement include:
- Earthquakes: Sudden slips along faults within the Earth release energy in the form of seismic waves that cause shaking and movement of the ground surface. These movements can be intense and sudden.
- Tectonic Plate Movement: The Earth's surface is divided into tectonic plates that slowly move due to forces such as mantle convection, ridge push, and slab pull. This movement causes deformation and movement of the ground over time.
- Ground Subsidence and Collapse: This happens when subterranean cavities (natural or artificial) cause the surface to sink or collapse suddenly, creating ground movement.
- Landslides and Rockslides: Movement of rock or soil masses down slopes due to erosion, saturation with water, or instability causes ground movement.
- Soil Expansion and Shrinkage: Variations in water content in clay-based or expansive soils cause the ground to swell or shrink, affecting stability and causing movement.
- Changes in Water Table or Drainage: Water saturation or drying can cause soil to expand, contract, or settle, leading to movement and affecting foundations.
Thus, the ground moves due to a complex combination of geological processes like earthquakes and tectonic activity, as well as surface and subsurface changes related to water, soil composition, and human activities. The scale of ground movement ranges from rapid, violent motion during quakes to slow subsidence or heaving caused by soil and water changes.